The present invention relates to CATV systems, and more particularly to a channel selecting device for CATV terminal units in which received channels can be indicated by the display of an arbitrarily selected number.
A conventional channel selecting device for CATV terminal units is embodied in the system shown in FIG. 1. In FIG. 1, a CATV signal is applied to an INPUT terminal, and the TV signal is provided at an OUTPUT terminal through a converter 1 and a descrambler 2, which are under the control of a microcomputer 4. An FSK signal is branched from the signal at the INPUT terminal and applied to an FSK signal receiver 3 where it is demodulated. The output signal of the FSK signal receiver is applied as data to the microcomputer 4. The microcomputer 4 is connected through bus lines to a program ROM 5 and a RAM 6 backed up by a battery 7.
In this system, to set the displayed channel numbers with respect to the received channels, an FSK signal is transmitted from the CATV control center indicating this information, and the data of this signal, demodulated by the FSK signal receiver 3, is stored as a table in the RAM 6 under the control of the microcomputer 4.
For example, if the subscriber operates a remote console to select displayed channel "33", the microcomputer 4 refers to the table stored in the RAM 6 to determine the signal of which received channel should be passed to the television receiver, here assumed to be that of a channel WWCH, and thus tunes the converter 1 to pass the signal from the channel WWCH to the television receiver. If the channel WWCH has been scrambled, a descramble signal is applied to a cause the descrambler 2 to descramble the TV signal.
In the above-described system, a data string as long as 15 bits, for instance, must be stored for each of the channels which can be received; that is, a considerably large quantity of data must be stored. Accordingly, the reading and writing of this data require a relatively long period of time, and the RAM necessarily must have a large capacity, and hence it occupies a large area.